Final answer:
The instrument that portrays the actual bank and pitch of the aircraft is the artificial horizon or attitude indicator.
Step-by-step explanation:
The instrument that should always be used if available to instantly portray the actual bank and pitch of the aircraft is the artificial horizon or attitude indicator. This instrument is found in the cockpit of an aircraft and provides information about the orientation of the aircraft relative to the horizon. It displays the pitch and bank angles of the aircraft, allowing the pilot to maintain the desired attitude and avoid dangerous situations.
The artificial horizon operates using a gyroscope, which is a spinning wheel that maintains its orientation in space. It is not affected by external forces and provides accurate information about the aircraft's attitude.